The present invention relates to a timepiece comprising a time display unit for displaying time and a calendar, and a solar cell for generating electric power utilizing light as an energy source, wherein electric power generated by the solar cell is used as an energy source for displaying time on the time display unit.
A battery has been in use traditionally as a power source of an electronic wrist watch and the like, however, owing to inconvenience in replacement of the battery and needs to overcome environmental pollution problems and so forth caused by waste batteries, there has recently come to be commercially available and in widespread use an electronic wrist watch wherein needs of replacing a battery are eliminated by assembling therein a solar cell, a secondary cell, and a charge-discharge control circuit for the secondary cell.
With a timepiece incorporating such a solar cell as power generation means, electric power generated by the solar cell through conversion of radiated optical energy into electric energy is stored in the secondary cell, and a clock circuit and so forth, and a stepping motor or a liquid crystal display panel are driven by the electric power as stored, thereby displaying time and calendar information in the form of analog display by use of a dial and hands, or digital display by use of the liquid crystal display panel.
The solar cell incorporated in such a timepiece is provided with power generation units, each formed by a first electrode, an optical power generation layer, and a second electrode that are stacked up in that order on a solar cell substrate in such a way as to be superimposed on each other. The solar cell substrate has transmitting portions, however, the transmitting portions are provided for the purpose of separating the power generation units from each other or connecting the same with each other, but not for positively ensuring transmitting property.
Accordingly, assuming that the visible side (a viewer""s side) of a time display unit of the timepiece is referred to as the front side while the back cover side thereof is referred to as the rear side, the solar cell is generally disposed on the rear side of the time display unit, or on the periphery thereof.
Further, a configuration of the timepiece has been proposed such that in order to shield a color of the solar cell substrate detrimental to a design feature of the timepiece incorporating the solar cell, or to shield a pattern of the power generation units, a shielding film such as a white diffusing film, a color diffusing film, a color filter, and so forth are disposed on the front side of the solar cell substrate, thereby shielding the solar cell substrate so as not to be directly visible.
In the case of installing the solar cell on the underside of the time display unit of the timepiece, however, it becomes necessary to keep a proper balance between the design feature and power generation efficiency because the solar cell substrate becomes visible through the time display unit or the shielding film is used on top of the solar cell substrate in order to shield the solar cell substrate. Use of a shielding film having a large optical absorption coefficient results in considerable deterioration of the power generation efficiency while use of a shielding film having a small optical absorption coefficient results in deterioration of the shielding effect of the solar cell substrate.
Further, in the case of installing the solar cell on top of the time display unit, the design feature of the timepiece would be largely dependent on a color and shape of the power generation units because, in this case, the transmitting portions only are installed over the time display unit without the power generation units installed thereon, and the power generation units are installed on the periphery of the time display unit for generation of electric power.
In this case as well, it is possible to shield a color tone or the pattern of the power generation units by installing a shielding film on top of the power generation units of the solar cell, however, in such a case, due to an increase in the difference of transmittance between the surface of the time display unit and the power generation units, the power generation units of the solar cell is distinctly recognized against the transmitting portions thereof, thereby subjecting the design feature of the timepiece to some constraints.
The invention has been developed to solve the problems described above encountered in the case of a timepiece provided with a solar cell, and it is therefore an object of the invention to provide a timepiece wherein visibility of a time display unit is not impaired even if the solar cell in whole, including power generation units, is installed on the visible side of the time display unit of the timepiece, and power generation units can be rendered inconspicuous so as not to introduce restrictions on the design feature of the timepiece even if no shielding film is installed, while ensuring satisfactory power generation efficiency of the solar cell.
To this end, a timepiece according to the invention comprises a time display unit, and a solar cell comprised of a solar cell substrate, and a power generation unit having at least a first electrode, a photovoltaic layer, and a second electrode, stacked up in that order so as to be superimposed on each other on the solar cell substrate, using electric power generated by the solar cell as an energy source for executing time display in the time display unit; said solar cell comprising a plurality of patterned power generation units provided on the solar cell substrate composed of a transparent material, and transmitting portions having a large transmittance in the visible light range and provided between the plurality of the patterned power generation units, wherein the solar cell is disposed on the visible side of the time display unit so as to be superimposed on the time display unit, the power generating units and the transmitting portions are superimposed on the time display unit, and the time display region is rendered to be recognized through the transmitting regions.
In the case of the time display unit being an analog time display unit having a dial and hands, the solar cell may be disposed on a visible side of the dial.
Or the solar cell may be disposed between the dial and the hands.
Otherwise, the solar cell is preferably provided with the plurality of the patterned power generation units being connected with each other via the respective first electrodes and the respective second electrodes, and the solar cell is preferably disposed between the time display unit and a glass of the timepiece so as to be superimposed on the time display unit.
The solar cell may have regions where transmittance of partial power generation and transmitting units comprised of the respective power generation units in combination with the respective transmitting portions is in a range of 30 to 80%, thereby enabling a condition on the underside of the solar cell substrate to be seen in the regions from a viewer""s side.
Further, the solar cell may be constructed such that an area ratio of the respective power generation units installed on the solar cell substrate to the respective transmitting portions adjoining the respective power generation units varies depending on a region on the solar cell substrate.
The solar cell may be constructed such that a plurality of solar cell substrates which vary in area ratio of the respective power generation units installed thereon to the respective transmitting portions adjoining the respective power generation units, are disposed therein.
Otherwise, the solar cell may be constructed such that a plurality of solar cell substrates, each having the power generation unit and the transmitting portion, are stacked up one after another, and are disposed such that transmitting portions of the plurality of the solar cell substrates are superimposed on each other.
A printed layer having numerals or letters may be provided on the solar cell substrate. The printed layer may be a printed layer printed with a plurality of colors.
The solar cell may comprise a design printed layer having numerals or letters provided on the solar cell substrate, and a printed layer provided on the dial as well, the design printed layer on the solar cell substrate and the printed layer on the dial may be disposed so as to be substantially superimposed on each other, and a spacing to the extent of a thickness of the solar cell substrate may be provided between the design printed layer on the solar cell substrate and the printed layer on the dial, so that the printed layer on the dial is rendered recognizable from the visible side through the transmitting portion of the solar cell substrate.
The respective power generation units and the respective transmitting portions provided on the solar cell substrate of the solar cell are preferably disposed repeatedly in the pattern of stripes, and a repeat pitch of the pattern of the stripes may be varied.
At least a portion of the power generation unit provided on the solar cell substrate may incorporate shapes of numerals or letters.
The plurality of the power generation units and the transmitting portions provided on the solar cell substrate of the solar cell may be patterned in concentric circles, and each of the plurality of the power generation units may be in the shape of a concentric circle cut at a part thereof, the plurality of the power generation units being mutually connected with each other at the cut part of the respective concentric circles.
Or the plurality of the power generation units may be formed in a spiral pattern on the solar cell substrate of the solar cell.
The first electrode and the second electrode, installed on the solar cell substrate of the solar cell, composing the power generation unit, may be connected with a clock circuit substrate for causing the time display unit to execute time display via an electrically conductive rubber, a flexible printed circuit board, a spring, or the like that is disposed so as to pass through a spacing between a side of the time display unit, and the inner side wall of a timepiece case.
The timepiece according to the invention may be a combination timepiece comprising the time display unit comprised of both an analog time display unit for displaying time with the hands and the dial, and a digital time display unit for displaying time and a calendar with numerals.
In such a case, the digital time display unit may be composed of a liquid crystal display panel.
For the liquid crystal display panel, use is preferably made of one comprising a reflection type polarizing film having one polarization axis which is a transmission axis and the other polarization axis which is a reflection axis substantially orthogonal to the transmission axis.
A light source is preferably installed on a side of the liquid crystal display panel, opposite from the visible side, as this will enable a viewer to recognize time display even in a dark environment, thereby enhancing usefulness of the timepiece.
The solar cell substrate needs to be provided with a through-hole through which a hand shaft serving as a rotatory shaft of the hands is penetrated
A printed layer is preferably provided around the through-hole in the solar cell substrate so as to shield the through-hole.
The solar cell substrate is preferably provided with an alignment portion used for alignment.
Further, the printed layer having numerals or letters is preferably provided on the solar cell substrate, and the alignment portion used for alignment with the time display unit is preferably provided on the solar cell substrate.
A repeat pitch or a repeat direction of the respective power generation units as well as the respective transmitting portions provided on the solar cell substrates is preferably differentiated from a direction of a display part provided on the time display unit or a pitch of a printed layer for prevention of occurrence of moire fringes.
The power generation unit of the solar cell is preferably installed on a face of the solar cell substrate, on a side thereof, facing the time display unit.
A pad electrode serving as a terminal of the first electrode and the second electrode, respectively, composing the power generation unit is preferably installed on a face of the solar cell substrate, on a side thereof, facing the clock circuit substrate.
A protective layer or a protective film is preferably provided on at least either of the front and rear faces of the solar cell substrate.
Either of the front and rear faces of the solar cell substrate is preferably stuck onto a glass of the timepiece to enhance durability of the timepiece.
An anti-reflection layer is preferably installed on at least the transmitting portion of the solar cell substrate.
An optical guide film or a lens for effectively radiating light to the power generation unit may be installed between the solar cell substrate and the dial.
The surface of the dial preferably has a rough face formed for effectively radiating light to the power generation unit of the solar cell substrate.
The surface of the dial may be provided with the printed layer formed for effectively radiating light to the power generation unit of the solar cell substrate.
Two types of solar cells, one of which has an area ratio of the power generation unit to the transmitting portion installed on the solar cell substrate differing from the same of the other, may be installed across the time display unit on both sides thereof.
Thus, with the solar cell for use in the timepiece according to the invention, a power generation unit provided on the solar cell substrate is divided into smaller units, and a transmitting portion having a transmittance of visible light larger than that for the respective power generation units, between the respective power generation units is provided thereby forming partial power generation and transmitting units having transmitting property.
Further, the more a transmittance of the partial power generation and transmitting units comprised of the respective power generation units and respective transmitting portions is enhanced, the more visibility of the time display units can be enhanced, and the more visibility of the power generation units can be lowered, however, power generation efficiency of the solar cell deteriorates.
Conversely, the more the transmittance of the partial power generation and transmitting units is lowered, the less a quantity of external light falling on the time display units becomes, thereby indicating darker display, and lowering the visibility of the time display units while increasing the visibility of the power generation units, however, the power generation efficiency is enhanced.
Accordingly, taking into consideration the visibility of the time display units indoors, the power generation efficiency, and power consumption of the timepiece, it is desirable to set the transmittance of the partial power generation and transmitting units in a range of 30 to 80%.
Further, by providing regions where the transmittance of the partial power generation and transmitting units varies depending on a design and display contents of the time display units installed on the rear side of the solar cell, an area ratio of the transmitting portions may be increased in parts where importance is attached to brightness, and an area ratio of the power generation units may be increased in other parts where importance can be attached to the power generation efficiency, thereby optimally setting the design feature and the power generation efficiency.
The respective transmitting portions provided between the plurality of the power generation units, installed in the partial power generation and transmitting units may be formed in the pattern of stripes, spirals or concentric circles, thereby rendering the solar cell substrate suitable for a design of the timepiece.
Further, by varying a pitch or width of the pattern in which the plurality of the power generation units are formed, occurrence of interference fringes caused by the pattern described above together with display on the rear side of the solar cell substrate can be prevented.
In the case of forming the printed layer having numerals or letters on the solar cell substrate, or forming numerals or letters by the power generation units, it becomes necessary to align the solar cell substrate with other parts of the timepiece, and accordingly, the solar cell substrate is preferably provided with the alignment portion. The alignment portion may be formed by the printed layer provided on the solar cell substrate. Or the solar cell substrate may be provided with a recess and a protrusion, a hole, or a notch as the alignment portion.